Chewable articles for pets such as dogs are well known in the art. These articles are of a flexible nature and serve as a toy for the pet as well as a means of keeping the pet's dentures in good condition. This type of article can be manufactured of different materials. Mainly, they can be divided in two classes: a non-edible variant and an edible variant.
The non-edible variant of a pet chew can be made from synthetic plastic materials or from raw hide. They have good chewing qualities and, due to their mechanical properties, they have a fairly long lasting time. The greatest disadvantage of most of the non-edible chews is that they are hardly biodegradable and/or digestible, if at all.
Edible pet chews are mostly produced from raw materials such as cereals, rice, milk, slaughterhouse by-products and products derived therefrom such as casein, gelatin, and starches and are by definition biodegradable and may provide nutritious value. Typically, they comprise numerous additives such as gums, meat or other products of animal origin, mineral oils or fats, vitamins, coloring agents, aromas or taste enhancers. The aim is, of course, to produce a coherent product having the desired mechanical properties to last a long time.
Of the known developed compositions for use as an edible pet chew, most are either based on starch, protein, or mixtures thereof.
U.S. Pat. No. 6,379,725 and WO 01/45517 disclose protein-based products, that is, products having a binding matrix essentially consisting of protein.
Starch-based products, that are products having a binding matrix essentially consisting of starch, are also described in the art.
A problem with starch-based compositions is that they readily dissolve in water, which means that during chewing, they become very “mushy” and consequently have a short chew live.
U.S. Pat. No. 5,827,565 discloses a dog chew based on a thermoplastic potato starch, PARAGON IM 1010. This thermoplastic starch comprises a fairly large amount of calcium carbonate. The dog chew has a brittle character and is therefore less suitable for dogs. A disadvantage of most known edible chews is that their mechanical properties are not satisfactory. Due to the fact that they comprise a mixture of several ingredients, they are often brittle and often fall apart soon after a pet, such as a dog, has set its teeth in it.
Starch-based products readily dehydrate if exposed to (dry) air resulting in products that can splinter or shatter and cause danger to the animal. According to US 2003/168020 it is the crystalline nature of the starch polymers that causes this shattering or splintering, and it is proposed that converting the crystalline starch to gelatinized nature solves this problem. US 2003/168020 discloses starch containing pet chews wherein mixtures comprising wheat flour, rice flour or tapioca flour in combination with a small amount of extra protein are extruded. Very little details are provided about the process or the resulting products.
US 2003/0219516 describes pet chews and methods for their manufacture based on potato starch, wherein a starch-based mixture is extruded to a thermoplastic mass which is subsequently moulded into a desired shape by injection moulding.
Thus, compared to a protein-based product, a starch based product requires specific production steps wherein the starch is gelatinized or destructurized. When combined with specific contents of plasticizers and fibers this will result in a non-cellular, flexible pet chew product which is dimensionally stable.
The present invention aims to provide a pet chew prepared from natural materials of renewable sources, making the chew both edible and biodegradable. It is specifically desired that the chew has excellent mechanical properties giving it a long lasting time, even if used for strong animals such as large dogs.
With respect to mechanical properties and other structural characteristics, it should be noted that WO 01/45517 discloses materials having a tensile strength of 1-5 Mpa (145-725 psi) and that US 2003/168020 discloses materials having tensile strengths ranging from 132 to 1724 psi (1-12 MPa). Thus, the manufacture of pet chews over a range of tensile strengths is in principle available in the prior art. However, there still is a requirement for processes for the production of pet chew products based on thermoplastic starch of high tensile strength.
In addition to a certain tensile strength there is a tendency towards preference for products that are softer, i.e. towards products with a lower E-modulus. It would be preferred if the tensile strength is not too much compromised thereby.
In addition to tensile strength and E-modulus, there is a requirement for esthetic surface characteristics. Detailed surface features and intricate designs of the pet chew will be lost of the texture of the final product is too coarse or if the amount of shrinkage after injection moulding is too large. Therefore, there is a requirement for pet chew products based on thermoplastic starch which have a fine texture, which do not suffer from excessive shrinkage after moulding and wherein detailed surface features and intricate designs are maintained